What is the definition or description of: food intolerance?

Not an allergy: Sensitivity means allergy. Intolerance means something else - usually an inability to digest a component of the food in question. If you are intolerant to cow's milk it could be because you can't digest milk sugar also called lactose. That is called lactose intolerance which is due to lack of an enzyme that digests the milk sugar. The enzyme is called lactase.